1. Field of the Invention
This invention pertains to a windshield wiper assembly of the type employed on motor vehicles.
2. Description of the Prior Art
At high vehicle speeds, the air impinging upon the windshield streams upwards and on both sides away from the windshield, such that it creates a lifting force on wiper blades and wiper arms. Thereby the contact pressure between windshield and wiper blade is reduced so that, especially in the lateral, intensely curved areas of the windshield, the cleaning effect of the windshield wiper installation is diminished. For safety, it is important that proper cleaning of the windshield is ensured at high driving speeds.
To avoid the lifting effect on the wiper blades, it has priorly been suggested to attach spoilers or other draft deflectors to the wiper blades and/or wiper arms to create an additional pressure directed against the lifting force. Because the surfaces of these draft deflectors must be small, they have only a slight effect. Such a solution is not advantageous from an aesthetical point of view.
It is known from German Pat. No. 2,314,724 to vary the pressure which the wiper arm, via the wiper blade, exerts on the windshield by means of a control cam attached on a disk. The disk is rotatably mounted on the wiper shaft and the curvature of the control cam is adapted to the windshield. The movement of a reversing bolt sliding on the control cam is transmitted to the holding pin of the wiper arm spring via a transversal pin and a wire yoke. Such a device is adapted to the windshield curvature but does not compensate for the lifting force created by the flow of air at high driving speeds.
In another known type of design (DE-AS No. 1,555,256), the contact pressure is increased by a two-armed lever mounted on the hinge pin which connects link and fastening members together. One arm is held on the wiper arm. The other arm is supported on the front surface of a wedge-type disk rotatably mounted on the wiper shaft, whereby said wedge-type disk is axially displaceable. By twisting a matching wedge-type disk from the interior of the vehicle by means of a traction rope, the upper wedge-type disk is axially displaced and thereby the pressure of the wiper blade on the windshield is varied. The curvature of the windshield is taken into consideration in that the front surface of the upper wedge-type disk has a cam contour adapted to the curvature of the windshield and the one arm of the lever rolls along said cam. In this assembly, the reversing element, that is, the lower wedge-type disk, is adjustable, whereby in addition to the normal spring pressure, a pressure is exercised on the wiper arm via the lever.
The effectiveness of the lever may be reduced under unfavorable weather conditions, e.g. ice and snow, by wedging of ice pieces and dirt between its arms and the wiper arm portions. At high driving speeds, the contact pressure of the wiper blade on the windshield is diminished thereby inhibiting effective cleaning of the windshield. Furthermore, the wedging of ice and dirt may be such that the lever will not reset.